[Docs] Add dev docs for sharing saved objects

[jportner]

In the 8.0 release, we updated most "isolated" saved object types to become "share-capable": #100489

In the 8.2 release, data views have been further changed to become fully "shareable": #123991

Now that data views are shareable, other saved object consumers which rely on data views will be able to start implementing shareable saved objects too. We have a developer guide but it doesn't include info on what changes need to be made to make a share-capable object type into a fully shareable one. There is a placeholder for this:
https://www.elastic.co/guide/en/kibana/8.0/sharing-saved-objects.html#sharing-saved-objects-step-6

We need to fill in this docs section with a concrete example and guidance on different considerations.

[elasticmachine]

Pinging @elastic/kibana-security (Team:Security)